This type alows you to model information which takes one of predefined values. There is not really an enumerated type (like BOOLEAN could be); instead, you can define your own one, such as:

Although the notation is simmilar to notation of integers with distinguished values, there are some important differencies, besides the use of keyword ENUMERATED:

Thus it is purely correct to ommit those numbers in definitions. On the other hand, numbers are included, because of compatibility.